shallow groundwater in sub-saharan africa: neglected opportunity

1

Shallow groundwater in sub-Saharan Africa: neglected opportunity 1

for sustainable intensification of small-scale agriculture? 2

John Gowing1, Geoff Parkin2, Nathan Forsythe2, David Walker2, Alemseged Tamiru 3

Haile3, Demis Alamirew4 4

1. School of Agriculture, Food & Rural Development, Newcastle University, Newcastle upon 5

Tyne, NE1 7RU, United Kingdom 6

2. School of Civil Engineering & Geosciences, Newcastle University, Newcastle upon Tyne, 7

NE1 7RU, United Kingdom 8

3. International Water Management Institute, P.O. Box 5689, Addis Ababa, Ethiopia. 9

4. Geological Survey of Ethiopia, P. O. Box 30912, Addis Ababa, Ethiopia 10

Correspondence to: [email protected] 11

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Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2015-549, 2016Manuscript under review for journal Hydrol. Earth Syst. Sci.Published: 19 January 2016c© Author(s) 2016. CC-BY 3.0 License.

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Abstract 14

There is a need for an evidence-based approach to identify how best to support development 15

of groundwater for small scale irrigation in sub-Saharan Africa (SSA). We argue that it is 16

important to focus this effort on shallow groundwater resources which are most likely to be 17

used by poor rural communities in SSA. However, it is important to consider constraints, 18

since shallow groundwater resources are likely to be vulnerable to over-exploitation and 19

climatic variability. We examine here the opportunities and constraints and draw upon 20

evidence from Ethiopia. We present a methodology for assessing and interpreting available 21

shallow groundwater resources and argue that participatory monitoring of local water 22

resources is desirable and feasible. We consider possible models for developing distributed 23

small-scale irrigation and assess its technical feasibility. Because of power limits on water 24

lifting and also because of available technology for well construction, groundwater at depths 25

of 50m or 60m cannot be regarded as easily accessible for small-scale irrigation. We 26

therefore adopt a working definition of shallow groundwater as < 20 m depth. 27

This detailed case study in the Dangila woreda in Ethiopia explores the feasibility of 28

exploiting shallow groundwater for small-scale irrigation over a range of rainfall conditions. 29

Variability of rainfall over the study period (9% to 96% probability of non-exceedance) does 30

not translate into equivalent variability in groundwater levels and river baseflow. 31

Groundwater levels, monitored by local communities, persist into the dry season to at least 32

the end of December in most shallow wells, indicating that groundwater is available for 33

irrigation use after the cessation of the wet season. Arguments historically put forward 34

against the promotion of groundwater use for agriculture in SSA on the basis that aquifers are 35

unproductive and irrigation will have unacceptable impacts on wetlands and other 36

groundwater-dependent ecosystems appear exaggerated. It would be unwise to generalise 37

from this case study to the whole of SSA, but useful insights into the wider issues are 38

revealed by the case study approach. We believe there is a case for arguing that shallow 39

groundwater in sub-Saharan Africa represents a neglected opportunity for sustainable 40

intensification of small-scale agriculture. 41

42

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1. Introduction 44

1.1 Context 45

There is abundant groundwater in Africa; more than 100 times the annual renewable 46

freshwater resource and 20 times the amount of freshwater stored in lakes (MacDonald et al., 47

2012), but its productive use for irrigation in sub-Saharan Africa (SSA) remains low. 48

Examining the evidence on use of groundwater for irrigation in SSA, Pavelic et al. (2013) 49

argued for action to unlock its potential for improving livelihoods of smallholder farmers. We 50

examine here the opportunities and constraints and draw upon evidence from Ethiopia to 51

demonstrate the case for action to promote use of shallow groundwater, in particular, for 52

small-scale irrigation in SSA. 53

54

Historically, groundwater exploitation has not been seen as an important component of water 55

resources development in SSA (Braune and Xu, 2010). Its contribution to rural water supply 56

is recognised, but groundwater has been seen more as a local resource, which supports 57

domestic demand, rather than as a strategic resource which can support productive use and 58

economic development. Arguments historically put forward against the promotion of 59

groundwater use for agriculture in SSA include that aquifers are said to be low in 60

transmissivity and that well yields are inadequate to support agricultural development at 61

scales larger than garden irrigation, particularly in the weathered crystalline basement rocks 62

that extend over about 40% of the African land mass (Wright, 1992; Chilton & Foster, 1995; 63

MacDonald et al. 2012). It has also been argued that groundwater use for irrigation will have 64

unacceptable impacts on wetlands and other groundwater-dependent ecosystems and on 65

domestic supplies (Adams, 1993; Giordano & Villholth, 2007; MacDonald et al., 2009). 66

67

However, the agenda has shifted and groundwater irrigation (GWI) by smallholder farmers is 68

increasingly being promoted by governments, donors and NGOs (Abric et al., 2011; CAADP, 69

2009; Chokkakula and Giordano, 2013). GWI is now seen as an important vehicle to 70

promote poverty alleviation, food security, rural employment, market-oriented agriculture 71

and climate change adaptation (Ngigi, 2009). Groundwater resources are ideally suited to 72

development of ‘distributed irrigation systems’ (Burney et al., 2013) in which farmers enjoy 73

far greater autonomy and flexibility of water supply than is possible through canal systems. 74


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Survey evidence shows that smallholder farmers prefer GWI (Abric et al., 2011; Giordano et 75

al., 2012; Villholth, 2013). 76

77

The global area equipped for irrigation has been estimated (Siebert et al., 2010) as 301 Mha, 78

of which 38% depends on groundwater. In SSA the extent of GWI is much less with only 6% 79

of the irrigated area reported by Siebert et al. (2010) and 10% by Giordano (2006) to be 80

supported by groundwater. However, a note of caution is necessary when considering official 81

statistics because of problems of definition and invisibility of so-called ‘informal irrigation’ 82

(Giordano, 2006; Frenken, 2005). Using evidence from various countries in SSA, Villholth 83

(2013) revised this estimate to 20% of the total irrigated area. Notable examples of public 84

sector initiatives exist, such as in the Fadama Development Programme in Nigeria (Abric et 85

al., 2011), but it is important to recognise the dominance of the informal sector, which is 86

characterised by autonomous farmer initiatives based upon the exploitation of shallow 87

groundwater resources. Such initiatives receive little official recognition and support 88

(Chokkakula and Giordano, 2013) and there is an urgent need to develop capacity for the 89

state to function in a dual role as facilitator and regulator of GWI. We argue that it is 90

important to focus this effort on shallow groundwater resources which are most likely to be 91

used by poorer rural communities in SSA. 92

93

1.2 Shallow groundwater: the opportunity 94

In the past few decades in Asia, a paradigm shift has occurred in irrigation practice, such that 95

distributed irrigation using privately owned wells and small motorised pumps has expanded 96

rapidly. This development has enabled smallholder farmers to diversify their farming systems 97

and grow high-value crops for the market. There is growing, but patchy, evidence that a 98

similar ‘irrigation revolution’ is happening in SSA (Dessalegn and Merrey, 2015). 99

100

Irrigation does not currently play a major role in African agriculture; the area equipped for 101

irrigation as a percentage of total cultivated land is 19.4 % globally, but only 3.3% for SSA 102

(Siebert et al., 2010), where agriculture remains almost entirely rainfed (You et al., 2010). 103

There have been many assessments of the irrigation potential (eg. Frenken, 2005) and 104

ambitious plans for its expansion, such as Commission for Africa (2010), which proposed 105

doubling the area under irrigation. In reviewing the investment needs on behalf of the World 106

Bank, You et al. (2010) examined biophysical and socio-economic factors affecting large and 107


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small-scale irrigation development. They found that small-scale irrigation offered far greater 108

potential than large scale; offering five times the expansion potential and double the 109

estimated rate of economic return. GWI can make an important contribution provided that the 110

focus is on shallow groundwater using technology that is accessible to small-scale farmers. 111

112

A simple typology of GWI is suggested by Villholth (2013) based on two key characteristics: 113

funding source (ie. private or public) and depth of groundwater (ie. deep or shallow). In most 114

parts of SSA existing GWI is privately funded and utilises shallow wells. It is used primarily 115

in high-value, market-oriented production (Shah et al., 2013) and women often play a 116

prominent role (van Koppen et al., 2013). 117

1.3 Shallow groundwater: anticipated constraints 118

Shallow groundwater is accessible to small-scale farmers with simple technologies for well 119

construction and water lifting and offers the best opportunity to develop low-cost GWI. 120

However, it is important to consider constraints since shallow groundwater resources are 121

likely to be vulnerable to over-exploitation and climatic variability. Villholth (2013) notes 122

that sustainable development of groundwater use for irrigation is limited by “replenishment 123

rates … extractability in some regions … and as a provider of environmental services”, and 124

argues that there is a need for understanding integrated groundwater and surface water 125

systems at different scales”. 126

127

Broad scale assessments of groundwater resource potential at national or continental scales 128

(e.g. MacDonald et al., 2012) and at sub-national scales (e.g. Awulachew et al., 2010) 129

provide an indication of the spatial extent and storage volume in aquifer formations, but an 130

assessment of the resource potential is critically dependent on understanding groundwater 131

dynamics. A recent review of groundwater conditions in 15 SSA countries concluded that 132

“information on aquifer characteristics, groundwater recharge rates, flow regimes, quality 133

controls and use is still rather patchy” (Pavelic et al., 2012b). There is widespread use of 134

shallow groundwater for domestic supply in most SSA countries, and indigenous knowledge 135

generally exists on the seasonal performance of wells during typical and drought years. 136

However, this knowledge is localised, qualitative and unrecorded. In contrast, there is 137

increasing availability of relevant global remote sensing data including topography, land 138

cover, soil moisture and climate products providing broad scale information that can be used 139

to estimate resource availability. 140


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141

Broad scale quantitative mapping of groundwater potential for Africa was revisited by 142

Altchenko and Villholth (2015) who considered the potential for sustainable GWI based on 143

renewable groundwater resources with 0.5o spatial resolution. They adopted an approach 144

based on conservative estimates of groundwater recharge and alternative scenarios for 145

allocation of groundwater to satisfy environmental requirements. They concluded that 146

throughout most of the Sahel and for the eastern tract of SSA from Ethiopia to Zimbabwe 147

renewable groundwater is under-exploited, and in some countries is sufficient to irrigate all 148

cropland. Any such assessment is subject to uncertainty and temporal variability of recharge 149

estimates. Due to the fragmented and localised nature of shallow groundwater resources 150

(Pavelic et al., 2012a) their capacity to buffer against inter-annual variability is expected to be 151

less than in the case of extensive deep aquifer formations. 152

153

As noted by Edmunds (2012), a major limiting factor is the need to identify whether the 154

stored groundwater is a renewable or a non-renewable resource, which depends on local 155

hydrogeological settings as well as regional climate. Therefore, there is a need to improve 156

understanding of available groundwater resources and to consider likely impacts of future 157

trends in climate and land use. In order to allow for balanced consideration of the 158

opportunities for and constraints to GWI from shallow aquifers in SSA, we report here a case 159

study in Ethiopia. We present a methodology for assessing and interpreting available shallow 160

groundwater resources and argue that participatory monitoring of local water resources is 161

desirable and feasible. We consider possible models for developing distributed GWI and 162

assess its technical feasibility. 163

164

2. Study area 165

The appropriate scale for the case study was considered to be a single administrative district 166

(known in Ethiopia as a woreda) as this allowed consideration of both technical and socio-167

economic aspects of groundwater resource assessment and management. In view of the 168

priority given to agricultural transformation in the area and availability of hydrogeological 169

data, the Tana basin was selected as a suitable site for the pilot study. Several woredas in the 170

basin were considered on the basis of their accessibility, the dominant farming system and 171


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their status within the agricultural growth strategy. Dangila woreda was selected as the case 172

study site (Figure 1). 173

Dangila woreda is situated in the north-western highlands with altitudes generally between 174

1850m to 2350m. Dangila town is situated along the Addis Ababa-Bahir Dar road at a 175

distance of 60 km south west of Bahir Dar. Part of Dangila woreda drains north-east towards 176

Gilgel Abay River and Lake Tana; the remaining area drains either west or south-west 177

towards Beles River, both of these are part of the Abay (Blue Nile) tributary of the River 178

Nile. The climate is sub-tropical with annual rainfall around 1600mm and the main rainy 179

season (known as Kiremt) occurring in June-September. 180

The total population of Dangila woreda is estimated at about 200,000 people in an area of 181

about 800 km2. Crop–livestock mixed subsistence farming is the primary source of 182

livelihood. According to a recent survey (Belay and Bewket, 2013) approximately 14% of 183

cropland is irrigated. This compares with estimates for Ethiopia as a whole of 1.8% by 184

Siebert et al. (2010) and 2.5% by Altchenko and Villholth (2015). Irrigation is mainly by 185

means of shared gravity diversions from seasonal and perennial streams, though there are 186

some reports of water lifting. There are many shallow (up to 12m) dug wells throughout the 187

woreda, but they are used primarily for domestic supply with only small pockets of garden 188

irrigation. There are some deeper drilled wells fitted with hand-pumps and some springs have 189

been developed for community water supply. 190

Ethiopia’s hydrogeology is complex. Basement aquifers, volcanic aquifers and Mesozoic 191

sediment aquifers are most extensive, but these are generally poor aquifers and consequently, 192

alluvial and/or Quaternary aquifers are more important. The geology is often highly varied 193

and, due to tectonic movement, areas with very shallow groundwater can occur alongside rift 194

areas with very deep groundwater. Kebede (2013) mapped the extent of alluvio-lacustrine 195

sediments in Ethiopia covering around 25% of the total land area. The alluvial deposits are of 196

two types: (1) extensive alluvial plains and (2) more localised strips of land and river beds 197

along rivers and streams occurring in most places both in the highlands and in the lowlands. 198

Existing mapping of shallow aquifers shows an extensive area of shallow regoliths to the 199

south of Lake Tana. The study site was selected to allow its exploration as a representative 200

shallow aquifer formation. 201

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Figure 1 here 204

205

At the case study site the geology consists of predominantly Quaternary basalt and trachyte 206

above Eocene Oligocene basalts and trachyte: the ages of these formations are taken from the 207

1:2,000,000 scale Geological Map of Ethiopia (Tefera et al., 1996). Outcrops are visible in 208

river beds and occasionally on steeper slopes and in a few man-made excavations. The 209

basalts are variously massive, fractured and vesicular with variations occurring over short 210

distances. The more massive basalt generally forms higher ground, with valleys and 211

floodplains overlying more fractured and vesicular basalt which is more easily weathered and 212

eroded. Above the solid geology lies weathered basalt regolith, itself overlain by red soils. 213

The red soils become more lithic and clayey with depth, grading into the regolith usually with 214

no obvious boundary. The regolith becomes greyer and stronger and has to be chiselled as it 215

deepens, though it is still quite friable. The most friable regolith is the result of weathering of 216

low-density vesicular basalt. 217

The superficial materials underlying the floodplains are often browner in colour, being more 218

organic-rich. Deep and wide desiccation cracks suggest a high clay content, though these 219

alluvial materials are occasionally very sandy and gravelly. The depth to the top of the solid 220

geology is highly variable. Wells are typically excavated until further excavation becomes 221

impossible, therefore the location of the rock-head can be inferred from well depth. The 222

rivers have often incised to the level of the rock-head, where solid basalt forms the river bed 223

with banks of only 1 to 3 m in height. 224

225

226

3. Feasibility of irrigation from shallow groundwater 227

Previous studies have estimated the extent of groundwater irrigation potential across SSA, 228

and most recently, Altchenko and Villholth (2015) identified the scope for developing small-229

scale GWI. They concluded that the semi-arid Sahel and East Africa regions offer appreciable 230

potential. In Ethiopia, their estimate of sustainable GWI potential based on renewable 231

groundwater was in the range 1.8 x 106

to 4.3 x 106 hectares (depending on provision for 232

environmental requirements). This represents at least a ten-fold increase on the current extent 233

of 117 x 103

hectares as estimated by Villholth (2013). However, assessment of potential 234


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based only on estimated recharge does not provide a reliable indication of the scope for future 235

expansion, which may be constrained by restrictions on access to the resource. The case study 236

site provides an opportunity to explore these constraints through a feasibility assessment. 237

Assessing technical feasibility of small-scale GWI involves balancing considerations of 238

water-table depth, well yield, technology (power) available for pumping, crop water demand 239

and area irrigated. 240

3.1 Depth to groundwater 241

Most of the literature on groundwater in SSA considers ‘shallow’ groundwater as any aquifer 242

up to 50 m or 60 m depth (Pavelic et al., 2012a). However, much of the existing small-scale 243

GWI depends on a water-table depth less than 5m. Because of power limits on water lifting 244

and also because of available technology for well construction, groundwater at depths of 50m 245

or 60m cannot be regarded as easily accessible for small-scale irrigation. We therefore 246

adopted a working definition of <20 m depth as also adopted by Villholth (2013). 247

Woldearegay and van Steenbergen (2015) adopted a working definition of <30 m depth for 248

shallow dug wells in northern Ethiopia. 249

3.2 Well yield 250

Typical well yields are reported (MacDonald et al., 2012; Pavelic et al., 2012a) as 1 – 5 l/s for 251

volcanic and consolidated sedimentary aquifers. Crystalline basement rocks have lower 252

yields, generally less than 0.5 l/s, though a significant minority of areas have yields that are in 253

excess of 1 l/s. There is a clear tendency for groundwater development to focus on deeper 254

aquifers with higher well yields. In northern Ethiopia, Woldearegay and van Steenbergen 255

(2015) reported that drilled wells constructed to 80 m or deeper were found to be highly 256

productive (well yield > 3 l/s). However, they also reported that many of these wells were not 257

operational and many were damaged. There is an apparent conflict between resource 258

potential and resource access and it is important to consider the constraint imposed by water 259

lifting technology. 260

3.3 Water lifting technology 261

Currently available options are rope and bucket (human power), treadle pump (human 262

power), chain-and-washer pump (human power), small centrifugal pumps (petrol or diesel 263

power), submersible pumps (solar power). Important considerations are (a) power available 264

for lifting water and (b) limit on suction lift. 265


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In the case of human power, a reasonably fit human can sustain a power output of 75W 266

(Fraenkel, 1986). The type of water lifting device makes little difference to power 267

requirement, but does affect ability to sustain it for long periods. The pumping rates which 268

can be achieved assuming a water lifting device with 50% efficiency are shown in Table 1. In 269

the case of animal power, capabilities of draft animals vary (Fraenkel, 1986). Assuming again 270

50% efficiency, Table 2 shows the pumping rates which can be achieved for various animals. 271

272

Table 1 here 273

274

Table 2 here 275

Small motorised pumps with rated power output of 0.5hp (375W) or 1hp (750W) are most 276

likely to be appropriate for petrol/diesel powered pumping from shallow wells. Costs are 277

currently around $250. Assuming 50% efficiency, it can be seen that pumping rates will be in 278

the same range shown above for animal power. However, it should be noted that actual 279

operating efficiency may be lower (perhaps 25%) for commonly available centrifugal pumps 280

because of the nature of the efficiency curve for such pumps. 281

282

The issue of limit on suction lift applies to any rotodynamic pumps (centrifugal or axial 283

flow). For such pumps the theoretical limit to suction lift is around 10m but the practical limit 284

is more like 7m where the pump is installed at sea level. Given that many applications in SSA 285

may be at altitudes up to 2000m, the limit on suction lift may be as little as 3m. Clearly this is 286

an important consideration for pumping from a well. A pump installed at the surface can be 287

used for only very shallow water-table conditions (say 3-5m depth). It may be possible to 288

modify well design to allow for the pump to be installed on a platform at an intermediate 289

depth, but practical considerations will still limit applications to water-table depths not 290

exceeding 10m, and this also represents a risk of aquifer pollution. 291

292

To avoid the suction lift constraint, alternative types of pump are required. Handpumps 293

installed on typical water supply wells are positive displacement (piston and valve type) 294

pumps. The Rower pump (Fraenkel, 1986) is a piston pump developed for irrigation use 295

which can deliver around 2.7 m3/h for a lift of 5-6m, which corresponds to the pumping rate 296

calculated above. The treadle pump (Kay and Brabben, 2000) is a reciprocating diaphragm 297

pump developed for irrigation use for which quoted delivery rate is again around 3m3/h for a 298


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lift of around 5m. Cost is comparable to a small motor pump at around $250. The main 299

difference between various types of hand pump appears to be mainly ergonomic such that the 300

ability to sustain pumping for extended periods may vary but rate of pumping stays much the 301

same. Motorised positive displacement pumps exist that could be used in principle but this 302

requires a long drive-shaft to deliver power from a motor on the surface. The alternative is to 303

use a submersible pump which uses an electric motor which is integral with the pump, both 304

being installed below the water-table. Availability of electrical supply to the well is an 305

obvious constraint on electric submersible pumps but solar power is becoming a feasible and 306

affordable option (Burney et al., 2010). 307

308

Matching the rate of pumping to well yield is another consideration in order to avoid 309

pumping the well dry. It will be seen that a well yield of 1 l/s does not represent a constraint 310

to human power water lifting but does become a problem with mechanically powered 311

pumping. Large diameter dug wells provide buffer storage which reduces the problem. 312

313

3.4 Crop water demand 314

Irrigation demand depends on crop type and local environmental conditions, but these do not 315

make a big difference when considering general feasibility. For the range of crops and 316

conditions likely to be encountered at typical GWI sites, a crop water demand of 5-8mm/day 317

can be assumed. Distance of delivery from the well to the crop will be short, so it is 318

reasonable to assume an irrigation efficiency of 80%. Under these assumptions, daily water 319

use (m3/day) can be calculated as shown in Table 3. 320

Table 3 here 321

It is apparent that human powered water lifting cannot irrigate more than 0.1ha for a water-322

table deeper than about 3m. For a water-table at 10m depth it requires 3 to 4 hours continuous 323

effort to irrigate an area of 0.1ha. This is consistent with expected limit on total human power 324

input of 250 to 300 Wh per day (Fraenkel, 1986). Animal power will allow an increase in the 325

area of irrigation to about 0.5ha. However the associated rate of pumping may exceed 326

expected well yield and the system may actually be limited by the aquifer rather than by 327

power for water lifting. 328

329


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Motorised pumps at 0.5hp (375W) deliver a flowrate very similar to what is achievable with 330

animal power and the same considerations therefore apply. However, long duration 331

continuous pumping is achievable, and it is feasible to irrigate up to 1 hectare from a single 332

well pumping from 20m deep. Motorised pumps at 1hp (750W) deliver a flowrate that is 333

above the expected yield from shallow aquifers. Continuous pumping from the well will 334

therefore not be possible in many cases. It will be desirable to adopt a well design that 335

increases yield (galleries) or provides storage (over-size well). In most cases there will be no 336

advantage in adopting a motorised pump rated at more than 0.5 hp (375 W). 337

338

A well yield of 3.6 m3/h is equivalent to continuous pumping at 1 l/s, which is a low rate for 339

efficient irrigation. Pumping to an above-ground storage tank will offer an improved system. 340

Modular drip irrigation kits (Burney et al., 2013) can overcome this limitation. 341

342

343

4. Assessment of the shallow groundwater resource 344

4.1 Methodology 345

Hydrogeological assessment 346

Hydrogeological assessments of the Dangila woreda were conducted between October 2013 347

and November 2015. The pre-existing geological map was reinterpreted on the basis of 348

observation of surface features combined with geophysical investigations and sampling from 349

dug wells and springs. Evaluation of the controlling factors for groundwater movement and 350

storage, and identification of geological structures (faults, lineaments, joints) and their role to 351

control flow direction in relation to the direction of major and minor structures was evidenced 352

by measurement or estimation of spring discharge, estimation of dug well yield based on 353

users’ information, and measurement of some stream flows. Rivers were walked in order to 354

accurately locate (using a GPS) perennial and seasonal reaches, and water depth, channel 355

incision and bank width was measured while geology of the river banks and river bed was 356

recorded. Transects were walked to ground-truth satellite land-use and vegetation type 357

imagery using Google-Earth imagery, which was found to be satisfactory for the purpose of 358

assigning land-use and vegetation type categories. 359

Based on geological/hydrogeological interpretation and field EC/pH measurements, sites 360

were selected for geophysical surveys using geoelectric soundings in a Schlumberger array. 361


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This investigation aimed at identifying the depth of possible deeper water bearing weathered 362

or fractured formations. 363

Selected dug wells were pumped and drawdown and recovery was monitored in order to 364

estimate aquifer hydraulic conductivity and specific yield, analysed using methods of 365

Moench (1985) and Barker and Herbert (1989). Tests were repeated in March (dry season) 366

and October (wet season) of 2015. Well tests were conducted on seven hand dug wells in 367

Dangila woreda. 368

369

Hydrometric data 370

Time series data were available from the national hydrometric network for the Kilti river 371

gauge at Durbete (Figure 1), and for rainfall and potential evapotranspiration from a 372

meteorological station near Dangila town. A 7-year period of daily data from January 1997 to 373

December 2003 was chosen for which almost complete data were available. The daily rainfall 374

amounts were compared against data from the Tropical Rainfall Monitoring Mission 375

(TRMM), to determine if they are likely to be representative of the spatial average over the 376

catchment area. 377

The river flow data were processed to identify baseflow using a standard flow separation 378

method (Tallaksen and van Lanen, 2004 ). Various other methods exist for flow separation, 379

but this provided a consistent approach to estimate the seasonal contribution from 380

groundwater to the river flow during years with different meteorological conditions. 381

382

Community-based mapping and monitoring 383

Following selection of the Dangeshta kebele (sub-district) as the focus site, gender-separated 384

focus groups were arranged with a Dangila woreda official. These involved firstly a 385

participatory mapping exercise of available local water resources and areas of land used for 386

pastoral and crop agriculture, followed by a broader discussion of existing understanding of 387

the hydrological system, current water use, and constraints and aspirations for agricultural 388

development. Subsequently, a small sub-group of the participants assisted in identifying 389

appropriate sites on two of the main river systems for monitoring river levels, as well as sites 390

for monitoring rainfall and groundwater levels. Two standard river staff gauges were installed 391

by the community, a suitable site was identified for installation of a non-recoding (manual) 392

raingauge and 5 shallow hand-dug wells were selected to be monitored using a dipmeter. 393


14

These activities were carried out by members of the community, from whom observers were 394

selected by the community to take daily readings. A workshop was then held to demonstrate 395

the equipment and its use to a mixed gender and age group audience. The installations and 396

training were carried out in February 2014, and daily monitoring has continued without 397

interruption and is still continuing up to and beyond the time of writing (November 2015). 398

This close engagement with the community has ensured that the equipment has been 399

protected as there is a sense of ownership by the community. Initial information arising from 400

the monitoring has been fed back to the communities with the aim of demonstrating the 401

usefulness of this level of quantitative understanding in order to ensure there is motivation for 402

continued monitoring. 403

404

4.2 Results of resource assessment 405

Hydrogeological assessments 406

Water-table depth is controlled by topography and geology with clear seasonal variations. 407

Near the end of the dry season in March/April within the floodplains, where the solid geology 408

is at a depth of around 4 m, the water-table lies at around 2 m. The water-table can often be 409

seen as a seepage face at this depth within river bank sections in alluvial sediment. However, 410

on the larger and steeper slopes where rock-head is around 15 m deep the water-table is at a 411

depth of around 12 m. 412

413

Despite the shallow aquifer being considered to be the weathered basalt regolith and alluvial 414

materials above the solid geology, it is possible that fractures within the solid geology are 415

influential to the hydrogeological regime. The geophysical surveys indicated that the 416

maximum depth of the weathered layer is around 30m, and that fractured zones may exist to 417

depths of 100-200m. Heterogeneities within the regolith, such as the clay content and the 418

fractured or vesicular nature of the pre-weathered rock, determine the productivity of a well, 419

though this is very difficult to estimate prior to excavation. Fissure flow in the deeper zones 420

is likely to be very restricted, as any fractures are probably filled with weathered material 421

with the same properties as the overlying materials. 422

423

From available geological mapping, four hydrogeological zones were initially identified 424

within Dangila woreda (Figure 2), which were defined by reclassification of an existing 425

geological map on the basis of their potential to support small-scale irrigation as follows: 426


15

Zone 1: High potential 427

Loamy soil underlain by sandy clay to depth of up to 4m. Regolith layer reaches 1.5m thick. 428

Localised pyroclastic fan deposits. High probability of well yield > 1 l/s. 429

Zone 2: Good potential 430

Alluvial material 1-2m thick underlain by sandy clay layer up to 3m thick. Regolith layer 431

reaches 1.5m thick. Weathered basalt with brown, grey and dark brown altered layers up to 432

25m thick. Good probability of well yield > 1l/s. 433

Zone 3: Moderate potential 434

Alluvial material 1 - 2m thick underlain by sandy clay layer 1 - 4m thick. Regolith layer 0.5 - 435

1.2m thick. Weathered Tertiary basalt up to 16m thick. High risk of well yield < 1 l/s. 436

Zone 4: Low potential 437

Sandy to silty clay soil 0.5 – 5.0m deep. Underlain by fresh to slightly weathered dominantly 438

massive trachyte of variable thickness. Very unlikely to achieve well yield > 1 l/s. 439

440

Figure 2 here 441

442

Following initial reconnaissance surveys and community workshops, it became evident that 443

topography has a significant influence on borehole locations and most likely also on well 444

yields. Lowland areas comprising expansive floodplains and low relief topography are 445

considered to be of high potential for productive groundwater use. A second map of 446

groundwater potentials was therefore produced based on surface topography (Figure 3), with 447

areas being defined by visual interpretation of satellite imagery. Comparison between Figures 448

2 and 3 shows broad similarities between the low groundwater potential zones in each map 449

which are generally located on higher ground near the catchment boundaries and along the 450

divide between the two main drainage areas within the woreda, and between the very high 451

potential zone in the geology-based map (Figure 2) and the high potential zone along the 452

valley draining to the south-west in the topography-based map (Figure 3). However, our 453

surveys, supported by further evidence given below, confirmed the importance of 454

topographic controls, so the other valley floors to the north-east of the topographic-based map 455

are also considered to be of relatively high potential (Figure 3). 456

457

Figure 3 here 458


16

459

Well tests were conducted on seven hand dug wells in Dangila woreda. Both the pumping 460

and the recovery data were analysed and provided consistent results confirming the suitability 461

of the methods. Hydraulic conductivity estimates ranged from 0.27 to 5.78 m/d in the dry 462

season and from 0.93 to 22.3 m/day in the wet season, which are typical values for weathered 463

basalt regolith. Specific yield estimations have a wider range and are more uncertain though 464

the mean value is as would be expected. A summary of the results is presented in Table 4. 465

They confirm that well yields of 1 l/s are achievable. 466

467

Table 4 here 468

469

The locations of the five wells and the raingauge monitored by the Dangeshta community are 470

shown in Figure 4, against the background of a Google satellite image. It is clearly evident 471

that these wells follow the general pattern of being mostly close to the edge of the 472

floodplains, where they remain accessible for the whole year, but are downslope from the 473

higher ground which provides recharge. 474

475

Figure 4 here 476

477

Records of groundwater levels and rainfall monitored by the local community for the period 478

April 2014 to November 2015 are shown in Figure 5. These show that only one of the wells 479

(MW1) dries out completely early in the dry season of 2014-15. Three of the wells (MW2, 480

MW3 and MW5) show similar behaviour, draining exponentially through most of the dry 481

season, with small but non-zero depths of water present throughout the season. Water depths 482

in well MW4 remain high through most of the dry season, before falling sharply in April/May 483

(there was a period of missing data during this time, but a similar pattern was observed in the 484

same months of the previous year). These data do, however, show that all the wells 485

maintained usable water levels into at least the end of December, and in some cases for 486

considerably longer. 487

488

Figure 5 here 489

490


17

Hydrological assessments 491

An assessment of the hydrology of the Kilti catchment (Figure 1) for the period 1997-2003 492

provides insights into groundwater availability within the wider catchment area. Rainfall data 493

for this period was compared with a longer record (1993 – 2014) of monthly rainfall in order 494

to allow an assessment of whether it reflected a sufficiently wide range of conditions. It was 495

found that 1999, 2000 and 1997 represent wet years (96% , 86% and 73% probability of non-496

exceedance respectively), while 2002 and 2003 represent dry years (9% and 14% probability 497

of non-exceedance respectively) and 1998 represents an average year (40% probability of 498

non-exceedance). The data for 1997-2003 therefore provide an adequate representation of 499

longer term variability. 500

501

Annual water balance components for the Kilti catchment are summarised in Table 5 and 502

shown in Figure 6. The catchment receives about 1600 mm/year of rainfall, of which about 503

200 mm/year enters the groundwater as recharge, discharging to the river as baseflow and 504

with a similar amount of rapid runoff contributing to a total river flow of about 400 mm/year. 505

It can be seen that the wettest year (rainfall 1960 mm) yields 12.8% baseflow, whereas the 506

driest year (rainfall 1350 mm) yields 15.8% baseflow. The lowest value of baseflow is 82% 507

of the mean baseflow which suggests a degree of buffering and indicates that groundwater is 508

available even in a very dry year. 509

510

Table 5 here 511

512

Figure 6 here 513

Mean monthly water balance components for the period 1997-2003 are summarised in Table 514

6 and shown in Figure 7. The shape of the annual Kilti hydrograph follows that of the annual 515

precipitation cycle. It can be seen that baseflow does not begin to recover until June, thus 516

indicating that groundwater recharge during Belg season (early ‘small’ wet season) is 517

minimal. However, there is evidence of baseflow persistence beyond the cessation of Kiremt 518

season (main wet season). Mean baseflows for 1997-2003 at the end of the months of 519

September to December are estimated as 8.8, 5.3, 2.1 and 0.93 m3/s respectively, following 520

an exponential decline indicative of natural drainage of groundwater within the catchment. 521

During the driest year of 2002 with rainfall non-exceedence of only 9% based on the long-522


18

term data, the baseflow at the end of December remained at 0.52 m3/s representing 43% of 523

the mean value for that date, indicating that groundwater remains available at this time even 524

during dry years. 525

526

Table 6 here 527

528

Figure 7 here 529

530

531

5. Discussion 532

In the past few decades in Asia, a paradigm shift has occurred in irrigation practice, such that 533

distributed irrigation using privately owned wells and small motorised pumps has expanded 534

rapidly. This development has enabled smallholder farmers to diversify their farming systems 535

and grow high-value crops for the market, thus bringing livelihood benefits whilst posing 536

challenges of resource management and governance. There is growing, but patchy, evidence 537

that a similar ‘irrigation revolution’ is happening in SSA (Dessalegn and Merrey, 2015). 538

There is an expanding literature on smallholder groundwater irrigation in SSA (Giordano, 539

2006; Giordano and Villholth, 2007; Siebert et al, 2010; Pavelic et al, 2013; Villholth, 2013; 540

Altchenko and Villholth, 2015). The focus has generally been on assessing potential at 541

country level and, as identified by Dessalegn and Merrey (2015), there is a need for these 542

broad evaluations to be supplemented by “localised and detailed assessments”. The case 543

study presented here for Dangila woreda in Ethiopia is an attempt to deliver such an 544

assessment. It would be unwise to generalise from this case study to the whole of SSA, but as 545

with the study of Fogera woreda, presented by Dessalegn and Merrey (2015), useful insights 546

into the wider issues are revealed by the localised case study approach. 547

This detailed case study has explored the feasibility of exploiting shallow groundwater for 548

small-scale irrigation over a range of rainfall conditions. Variability of rainfall (9% to 96% 549

probability of non-exceedance) does not translate into equivalent variability in groundwater 550

levels and baseflow. Groundwater levels observed in most shallow wells persist into the dry 551

season to at least the end of December, indication that water is potentially available for 552

irrigation use during the period after the cessation of the wet season (typically mid Oct). 553


19

Catchment baseflows also persist to at least the end of December, even during dry years, 554

indicating that groundwater is available more widely across the catchment during this period. 555

Well tests indicate that shallow wells (< 20m) can support abstraction rates of 3.6 m3/hr, 556

which are sufficient to support small-scale irrigation, at the end of the Kiremt wet season 557

from October to December. A single well can support irrigated cropping on a plot up to 1ha 558

provided that crops are planted sufficiently early to make use of rainfall in the later part of the 559

Kiremt season, and avoid the second part of the dry season when groundwater levels have 560

generally declined through natural drainage, and which may be required to support other 561

environmental requirements. 562

Understanding the resource is necessary, but not sufficient, to guarantee sustainable 563

management. Small-scale irrigation from shallow groundwater, like any other type of 564

irrigation development, should be seen as a socio-technical problem (Dessalegn and Merrey, 565

2015). This implies that the social dimensions of irrigation are as important as the technical 566

dimensions. Social dimensions include issues of governance such as organisation of water 567

use, collective action and conflict resolution. Technical dimensions in this case include issues 568

of resource assessment and water lifting. Sustainable development of small-scale irrigation 569

from shallow groundwater in SSA will require support from external agents (hydrogeologists, 570

irrigation experts etc), but most importantly will depend upon a devolved participatory 571

approach to local resource management at the community level. In the case of Ethiopia, the 572

woreda (ie. district) is the appropriate scale in that it provides the interface between local 573

communities and external agents. 574

There is a need for further action-research at this scale in places like Dangila woreda to 575

develop capacity for the state to function in a dual role as facilitator and regulator of GWI. 576

Community based monitoring (citizen science) has been shown to be valuable in providing 577

the data required for resource management while also providing an entry-point for external 578

agents. There is a case for investigating the feasibility of establishing a cadre of local ‘para-579

hydrologists’ to act as intermediaries between local communities and external agents in the 580

long term. Para-hydrologists are expected help ensure quality of community-led monitoring 581

data as well as to play a key role in facilitating bi-directional information exchange between 582

technical professionals and community members. Experience in India (Shah, 2007) has 583

demonstrated the value of providing an appropriate level of technical training in hydrology 584

and hydrogeology in promoting community level groundwater governance. 585


20

6. Conclusion 586

Shallow groundwater resources represent a neglected opportunity for sustainable 587

intensification of small-scale agriculture in SSA. Concerns over low aquifer transmissivity, 588

low well yields, aquifer vulnerability and resource conflict are exaggerated. Shallow 589

groundwater (< 20m depth) is accessible to small-scale farmers and should be seen as a 590

strategic resource. There is a need to develop capacity for the state to function in a dual role 591

as facilitator and regulator of GWI. However, the localised nature of shallow aquifers will 592

require an approach based around participatory resource management by local communities. 593

There is widespread use of shallow groundwater for domestic supply in most SSA countries, 594

and indigenous knowledge generally exists on the seasonal performance of wells during 595

typical and drought years. This knowledge is localised, qualitative and unrecorded, but it 596

provides an entry-point for a participatory approach. 597

We propose an approach to developing irrigation from shallow groundwater in SSA with a 598

focus on community-led adaptive resource management. This is based on two main premises: 599

• that a ‘bottom-up’ approach with close engagement between local communities and 600

professionals is necessary for development of shallow groundwater resources for small scale 601

irrigation; 602

• that an adaptive approach to integrated management of groundwater and surface water 603

resources is necessary for long-term sustainability, and this requires quantitative hydrological 604

monitoring at the local scale, particularly of groundwater levels. 605

606

Acknowledgements 607

This work was funded by the NERC/DfID UpGro programme under Grant NE/L002019/1. 608

We are grateful for the co-operation of many people and organisations in Ethiopia, 609

particularly the local communities in the Dangila woreda. Further details of the study are 610

available at http://research.ncl.ac.uk/amgraf. 611

612

613


21

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715

716

717


25

Figure and table captions 718

Figure 1. Case study site: Dangila woreda in Amhara region, Ethiopia 719

Figure 2. Groundwater potential zones, based on reclassification of geological map 720

Figure 3. Groundwater potential zones, based on topographic analysis 721

Figure 4. Locations of community monitoring wells and rain gauge 722

Figure 5. Daily community observed data for 2014-15: groundwater levels are plotted 723

relative to base of well to show water column depth (well depths are: MW1 6.00m; MW2 724

6.89m; MW3 4.18m; MW4 9.17m; MW5 8.44m) 725

Figure 6. Annual river discharge and baseflow for the Kilti catchment (1997-2003) 726

Figure 7. Mean monthly river discharge and baseflow for the Kilti catchment (1997-2003) 727

728

729

730

Table 1: Pumping rate for human-powered device operating at 50% efficiency 731

Table 2: Pumping rate for animal-powered device operating at 50% efficiency 732

Table 3: Daily water use (m3/day) under a range of irrigation demands at 80% efficiency 733

Table 4: Aquifer properties determined by well tests using methods of Moench (1985) and 734

Barker and Herbert (1989): hydraulic conductivity (K); specific yield (SY) 735

Table 5: Annual water balance data for 1997-2003 (mm) 736

Table 6: Mean monthly water balance data for 1997-2003 (mm/day) 737

738


26

739

740

Figure 1. Case study site: Dangila woreda in Amhara region, Ethiopia 741

742


27

743

744

Figure 2. Groundwater potential zones, based on reclassification of geological map 745

746


28

747

748

Figure 3. Groundwater potential zones, based on topographic analysis 749

750


29

751

752

Figure 4. Locations of community monitoring wells and rain gauge 753

754


30

755

Figure 5: Daily community observed data for 2014-15: groundwater levels are plotted relative 756

to base of well to show water column depth (well depths are: MW1 6.00m; MW2 6.89m; 757

MW3 4.18m; MW4 9.17m; MW5 8.44m) 758

759


31

760

Figure 6. Annual river discharge and baseflow for the Kilti catchment (1997-2003) 761

762

763

764

765

Figure 7. Mean monthly river discharge and baseflow for the Kilti catchment (1997-2003) 766

767

768


32

Head (m) 0.5 1.0 2.5 5.0 10.0 20.0

Rate (m3/h) 27.5 13.8 5.5 2.7 1.3 0.7

769

Table 1: Pumping rate for human-powered device operating at 50% efficiency 770

771

772

773

Animal Weight (kg) Power

(W)

Pumping rate (m3/h) at various heads

1.0m 5.0m 10.0m 20.0m

Mule

Donkey

Bullock/ox

350 - 500

150 - 300

500 - 900

300 - 600

75 - 200

300 - 500

54 - 108

13.8 - 36.8

54 - 90

10.8 - 21.6

2.7 - 7.2

10.8 - 18.0

5.4 - 10.8

1.3 - 3.7

5.4 - 9.0

2.7 – 5.4

0.7 – 1.8

2.7 – 4.5

774

Table 2: Pumping rate for animal-powered device operating at 50% efficiency 775

776

777

Irrigation demand

(mm/day)

Area irrigated (ha)

0.1 0.25 0.5 1.0

5 4.0 10.0 20.0 40.0

6 4.8 12.0 24.0 48.0

7 5.6 14.0 28.0 56.0

8 6.4 16.0 32.0 64.0

778

Table 3: Daily water use (m3/day) under a range of irrigation demands at 80% efficiency 779

780


33

Dry season Wet season

K (m/day) SY K (m/day) SY

Mean 2.10 0.097 8.79 0.074

Median 1.32 0.075 6.20 0.054

St Dev 1.84 0.095 7.52 0.112

781

Table 4. Aquifer properties determined by well tests using methods of Moench (1985) and 782

Barker and Herbert (1989): hydraulic conductivity (K); specific yield (SY) 783

784

785

786

1997 1998 1999 2000 2001 2002 2003 Mean

Rainfall 1667 1555 1959 1896 1411 1350 1369 1601

Potential

Evapotranspiration

1451 1425 1417 1416 1405 1415 1422 1422

Discharge 395 368 481 544 324 358 388 408

Baseflow 208 210 252 259 179 213 175 214

787

Table 5. Annual water balance data for 1997-2003 (mm) 788

789

790

791

792

J F M A M J J A S O N D Total

Rainfall 0.01 0.06 0.46 1.00 4.76 8.38 10.84 11.06 7.79 5.02 1.39 0.07 4.26

Evaporation 3.51 3.99 4.42 4.75 4.42 3.99 3.42 3.27 3.73 4.02 3.80 3.42 3.89

Discharge 0.11 0.06 0.03 0.03 0.12 0.85 2.75 4.14 2.73 1.67 0.61 0.20 1.12

Baseflow 0.09 0.05 0.02 0.01 0.03 0.21 1.12 2.08 1.74 1.00 0.44 0.18 0.58

793

Table 6. Mean monthly water balance data for 1997-2003 (mm/day) 794

795

796

797


shallow groundwater in sub-saharan africa: neglected opportunity

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